Foley's murder was shown in a video released by the Islamic State, an al-Qaida-inspired group that is also referred to as either ISIS or ISIL. The voice of the masked kidnapper has a distinctly British accent, leading intelligence officials to surmise he may have ties to the U.K.

"We're putting a great deal into the search," Westmacott said, referring to the use of voice analysis and other methods.

CNN reports: "Linguists said that based on his voice, the man appears to be young, most likely under 30. He also appears to have been educated in England from a young age and to be from southern England or London."

The Associated Press says: "British newspapers reported Sunday that investigators were looking at several British jihadi thought to be in the Raqqa area of Syria.

AP says one among the possibilities is Abdel-Majed Abdel Bary, who is a former rapper from London.

He "reportedly has joined militants in Syria. He is the son of Abdel Abdul Bary, an alleged al-Qaida operative who was extradited from Britain to the U.S. in 2012 to face terrorism charges," the news agency says.